* {
  margin: 0;
  padding: 0;
}
//公共样式
.parent {
  width: 200px;
  & > .submenu {
    display: none;
  }
  &:hover > .submenu {
    display: block;
  }
}
ul {
  margin-left: 15px;
  li {
    list-style: none;
  }
}
//让一级菜单元素水平排列
.nav-bar {
  display: flex;
  justify-content: space-around;
  //&等价于this指针
  & > li {
    & > span {
      background: #e3e3e3;
      color: white;
      padding: 2px 4px;
      border-radius: 4px;
    }
  }
}
